1. Field of the Invention
The present invention is directed to a process of measuring processing fluids dispensed in precision processing operations. More particularly, the present invention is drawn to a process of measuring processing fluids dispensed during in semiconductor processing.
2. Discussion of the Prior Art
In many processing operations sequential dispensing of process fluids occur. In most such cases the amount of fluid dispensed is critical to proper processing of the desired product. Moreover, continuous operation is also dependent upon precision dispensing of the process fluid. Of course, process fluid costs further emphasizes the criticality of precision dispensing of the fluid.
Semiconductor processing, wherein semiconductors are prepared, exemplifies such processing operations. In the manufacture of semiconductors sequential dispensing of fluids in continuous, automated processing occurs. It is to processes of this type that the present invention is addressed.
In semiconductor processing, lithography tools are essential for spin coating and developer applications. Amongst the process fluids dispensed in lithography tools are photoresist materials, antireflective coating materials, via fill/planarization materials, passivity materials, rinse solvents, developer solvents, adhesion promoters and the like. All of these materials are costly and their spillage represent an environmental hazard.
In addition to these requirements, it is essential for proper processing of a semiconductor wafer that the exact desired amount of the fluid compounds be dispensed in each step. The dispensing of these process fluids in excess of what is required for proper processing can result in costly over-utilization of the dispensed compound as well as increasing the chance of releasing hazardous waste into the environment. The dispensing of inadequate volumes of requisite process fluids, on the other hand, can result in product degradation and semiconductor failure.
At present, monitoring of process fluids for detection of improper fluids usage in precision processing operations is addressed by either direct measurement or by inference. In direct measurement, the precision processing operation is halted to permit such measurement. The processing equipment is inspected at the cost of extensive downtime and time consuming restart up operations.
If the second prior art detection method is elected, e.g. inference, structural defect data obtained using PLY (process limited yield) methods or electrical defect characterization data obtained using electrical testing is analyzed. This method is similarly faulty because inference methods rely on measurement, data collection, and data analysis at various stages between processing steps. This means that incorrect dispensing of process fluids will be detected much later after the fact. The mean-time-to-detect (MTTD) depends on what stages of the manufacturing flow these measurements are scheduled to take place. Furthermore, detection assumes the existence of sufficient control schemes and in many cases demands the appropriate reaction from human operators and engineers. By the time the problem is identified and corrective action is taken, several hundreds of product units may be already irreversibly damaged, resulting into yield degrades or scrapping of the defective product units. At best, the faulty products must be reworked at significant reprocessing costs.
These methods are well exemplified by semiconductor wafer manufacturing operations. Presently, chemical usage in such operations, when measured by direct volumetric measurement, requires labor intensive semiconductor tool downtime to permit that measurement. The tools are opened and exposed during the measurement. It furthermore requires FM (foreign material) monitors to run before they can be reused in production. Obviously, the semiconductor tools are unavailable for productive use during this period.
The second prior art method of detecting incorrect process fluid usage in semiconductor production processing, involves data analysis of problematic product using PLY and electrical characterization methods. This solution involves problem detection after semiconductor wafer production has been completed. Thus, if an error is found, the best outcome that can be accomplished is a rework of the semiconductor wafers produced therebefore, which significantly increases cost and reduces productivity.
In the worst case scenario, semiconductor wafer product lots have to be scrapped because the defects are catastrophic and cannot be reworked. This is so insofar as it can oftentimes be two or three days before semiconductor wafer defects are detected. Thus, semiconductor wafer loses can be very extensive. In this regard, it should be appreciated that detection depends on human response to PLY signals. Therefore, faulty human response can lead to further delays in detection and corrective actions. As a corollary, special training of personnel may be required.
The above remarks make it apparent that a processing scheme that automatically responds to too high or too low dispensed amounts of semiconducting processing chemicals, especially a processing scheme which would include appropriate warning signals, at the time and at the place where the chemicals are dispensed, would represent a significant processing advance. Such a system would eliminate production disruptions resulting from direct volumetric measurements or, alternatively, eliminate the possibility of large write-offs of inappropriately produced semiconductor product.
Attempts to monitor dispensed liquid in chemical processing operations have been attempted in the past. U.S. Pat. No. 4,844,297 describes a process and apparatus for dispensing a desired quantity by weight of a fluid material. In that disclosure, a dispensing system is employed wherein the weight of dispensed compounds through each dispensation line is weighed. In this system, fluid in each dispensing line is weighed to control or check the weight of chemical fluid dispensed and compared to the desired dispensing weight.
In processing operations requiring continuous sequential dispensing of process fluids, however, there are typically numerous dispensing lines making individual monitoring of each dispensing line highly complex, expensive and, oftentimes, even disruptive of satisfactory operation of the monitored process.
This analysis emphasizes the need in the art for a new, more improved process of monitoring dispensing of process fluids in precision processing operations.